Diodes are customarily used to rectify alternating currents; this is also true for rectifiers in motor vehicles, in which a rectifier bridge having a total of six power diodes is used to rectify the output currents supplied by a three-phase alternator. These power diodes are, for example, press-fit diodes, these being diodes which are pressed into a mount and thereby connected thereto.
Press-fit diodes for motor vehicle rectifiers are described, for example, in published German Patent documents DE 43 41 269 and DE 195 49 202. These publications describe the basic design features of plastic-sheathed press-fit diodes. These press-fit diodes include a chip which is connected to a head wire and a base via solder layers. The head wire and base are surrounded by a plastic sheathing which establishes a mechanical connection. The base includes a press-fitting area which deforms slightly when the diode is pressed into the rectifier.
FIG. 1 shows an example of a plastic-sheathed diode described in published German Patent document DE 195 49 202. The diode includes mainly a base 1, a sheath 2 and a chip 3 which is situated between base 1 and head wire 4. Chip 3 is permanently connected to both base 1 and head wire 4 via solder 5a, 5b. Parts of the diode may be coated with lacquer 6. A plastic sheathing 7 provides a mechanical grip and thus also establishes a permanent mechanical connection between base 1 and head wire 4.
The basic structure of a diode described above, for example a power diode which is pressed into a rectifier for a three-phase alternator in a motor vehicle, differs only slightly from other known diodes, e.g., press-fit diodes. However, the known diodes having this structure require a mounting height of at least 8 mm. Accordingly, there is a need for a flatter design that enables the diode to be used in generator constructions in which there is not enough space for mounting heights of more than 8 mm.
In this regard, other flat power diodes are known which have a mounting height of only 4 mm. These flat diodes include a housing having a cup-like shape which permits the reduced mounting height. When such known cup-type diodes are pressed into the rectifier sheet, the edge of the housing is inevitably deformed toward the inside, due to the press fitting between the diode and press-fit block, and presses upon the plastic sheathing protecting the chip.
To absorb or cushion this deformation, the plastic sheathing in such a known cup-type diode is made of a rubber-like soft casting compound, for example filled silicone. This results in the disadvantage that any tensile loads which may be present act directly upon the solder connecting the chip to the base and head wire, or upon the chip itself. To solve this problem, a strain relief may be provided in the head wire, which makes handling difficult during processing and requires additional operations. In addition, the elastic sheathing does not provide secure clamping of the diode base and head wire without additional measures, so that the solder and chip are not relieved by the sheathing in the event of temperature changes. Under some circumstances, this may result in a shorter diode life.